1. Field of the Invention
This invention relates to gate valves. In particular, this invention relates to gate valves which have a wedge-shaped valve member which includes an internal pressure equalizing valve for use in reducing the pressure differential between the upstream and downstream sides of the wedge-shaped valve member prior to opening of the gate valve.
2. Related Art
West German Patent No. 25 46 024.6 which issued on Apr. 21, 1977, to Klaus F. Union Armat discloses two inclined discs are in place of the wedge-shaped valve member with two smaller discs in the center providing a bypass path, all discs activated by the same valve stem. In this device the discs sealing surfaces are exposed to the flowing fluids, as the pressure equalizing valves are opened, the flowing fluids erode the sealing surface and the valve may not provide positive closure. Fluid buildup in the annular space above the discs may prevent the opening of both the bypass and the valve.
A wedge shaped gate valve which incorporates a pressure equalizing valve is disclosed in U.S. Pat. No. 4,678,008 issued on Jul. 7, 1987, to Gyongyossy. In this structure, the pressure equalizing valve is in the form of a piston. When the valve stem is cracked open, the system pressure will raise the piston from the seat to permit fluid to flow from the upstream side to the downstream side of the valve. Pressure buildup in the annular space could prevent the piston-shaped equalizing valve from opening, as equal pressures acting on both sides of the valve and the gate valve.
A common problem in gate valves is the accumulation of fluids in the annular space above the gate which can lock the gate down if such fluids are not removed or allowed to escape.
It is an advantage of the present invention to provide a simple and efficient pressure equalizing valve in a wedge-shaped valve member of a gate which will open freely and effortlessly without regard to the fluid pressures in the system.